Flexible joint for drill string



June .2, 1964 H. BLACK FLEXIBLE JOINT FOR DRILL STRING Filed April 27,1962 HA ROL 0 BL A CK IN VE N TOR M A T TORNEY U s t d S ates 1 P t n t3,135,103 FLEXIBLE JOINT FOR DRILL STRING Harold Black, Box 5053,Abilene, Tex.

7 Filed Apr. 27, 19 2, Set. No. 190,733 a 2 Claims. or. 54-11 Thisinvention relates to the rotary method of drilling wells and hasreference to a flexible joint to be located in a drill string forrelieving stress in pipe and drill collar connecting threads.

In rotary drilling the effectiveness of the drill bit on the formationbeing cut depends, to a large extent, on the weight of the drill stringapplied to the bit. Frequently, drill collars, that is, thick walllengths of tubing are threadedly connected in the drill string toincrease weight. The length of the drill string sometimes flexes in thebore hole and the flexibility of the connected lengths of drill pipeusually prevents damaging stress in the threaded pipe joints. However,since the drill collars have thick walls'the resulting stresses areconcentrated in the connecting threads which tend to break.

'It is an object of this invention to provide an intermediate sub withadded flexibility to be inserted at the joints between the drill collarsto relieve the strain concentrated at the drill collar threads.

It is a further object of the invention to provide a flexible connectionwhich will carry the torque load of the rotary drill without breakingthe solid steel to steel vertical contact through the threaded joints.

A further object of the invention is to provide a flexible joint whichwill prevent the drilling string from separating even though its torquetransmitting element is destroyed by overload or deterioration, andwhich will carry the Weight of the string below the joint when it isnecessary to pull the string from the well.

These and other objects of the invention will become apparent from thefollowing description and the accompanying drawings, wherein:

FIGURE 1 is a vertical cross section of the stress relieving sub betweenthe ends of the adjacent drill collars.

FIGURE 2 is a horizontal section taken on line 22 of FIGURE 1.

FIGURE 3 is a detail of the cross section similar to FIGURE 2, butillustrating a modification of the invention.

FIGURE 4 is a diagram exaggerating the bending of the drilling stringnear the bottom of the hole.

FIGURE 5 is a diagram exaggerating the bending of the drill string withthe invention included.

FIGURE 6 is a transverse section view similar to FIGURE 2 but showing afurther modified form of the invention.

As shown in FIGURE 4 the drilling string has a rotary rock bit 10attached to the end of a drill collar 11 which, in turn, is attached toa second drill collar 12. The drill string thereabove is not shown.

The diameter of the bore hole 13 is determined by the size of the bit 10and is larger in diameter than the drill collars 11 and 12 or any pipein the drill string so as to provide an annulus 14 therearound throughwhich the drilling fluid is returned to the earths surface after havingbeen pumped to the bit through a central bore extending through thedrill string including the drill collars as indicated at 15.

The upper and lower ends of the drill collars 11 and 12 have internaland external threads 16 and 17, and the assembled sub 18 comprising thepresent invention is connected therebetween.

The sub 18 includes a lower tubular portion 19 having threads 16a on thelower end thereof for engagement with the internal threads 16 in upperend of the drill collar 11 3,135,103 Patented JuneZ, 1964 therjebeneath,and a similar upper tubular portion 20 having threads 17a in the upperend thereof for engagement with the external threads 17 in the lower endof the drill collar 12 thereabove. The upper end ofthe lower part 19' ofthe sub 18 is provided with a cylindrical axial extension 21 which isretained within and spaced from a cylindrical axial socket 22 in thelower end of the upper part 20. The annulus between the extension 21 andthe socket 22 is filled with rubber 23 which is vulcanized or otherwisebonded to both parts of the sub 18. The transverse face 24 of the socket22 bears against the shoulder 24a at the base of the extension 21 andthe transverse face 25 of the extension 21 bears against the fiat bottom25a of the socket 22.

The rubber 23 allows for the bending of the sub 18 between its parts 19and 20 as shown by the exaggerated diagram, FIGURE 5, yet the bendingstrain transmitted to the threads 16 and 17 is not beyond theirstrength. The axial extension 21 is provided with radial round holes 26to receive the ends of inwardly extending plugs 27 held in the walls ofthe socket 22 by threads 28. The plugs 27 are spaced within the holes26, and which spaces are filled with the rubber 23. The torque of thedrilling operation is transmitted through the sub 18 by the shearstrength and the bond of the rubber 23. The plugs 27 and rubber 23 inthe holes lend a part in transmitting the torque and in case of thefailure of the rubber 23 through overloading or deterioration the plugsare left intact to bear against the upper surface 29 of the holes 26 andhold the string together while it is pulled from the well for repairs.

An alternate form of plug 27a is shown in FIGURE 3 which is weldedinstead of being threaded into the socket 22. The outer end of the plugmay be provided with internal threads 30 for attaching a tool, notshown, to remove the plugs for repairs to the sub 18 after cutting theweld 31.

The further modified form of the invention shown in FIGURE 6 shows anannular groove 32 in the extension 21 for receiving the inner ends ofthe plugs 27 which are spaced from the surfaces of the grooves and whichgroove is filled with rubber 23. While this form of the invention maynot carry the torque loads of the first form of the invention, but inthe event of failure of the rubber 23 the length of collars and drillstring below the sub 18 may be retrieved.

The invention is not limited to the exemplary construction herein shownand described, but may be made in various ways within the scope of theappended claims.

What is claimed is:

1. A flexible sub for connection in a drill string, said sub comprising:first and second axially aligned tubular members, a cylindricalextension of reduced outside diameter on an end of the first saidmember, a cylindrical socket Within an end of the second said member andreceiving said cylindrical extension, the axial length of said socketand said extension being substantially equal, the extending end of saidcylindrical extension being in substantial abutting contact with saidsecond tubular member, resilient material between the cylindrical wallof said socket and the cylindrical surface of said extension, and meanstransmitting torque loads from one said member to the other said member,said means being comprised of radially disposed pins carried by one ofsaid members and extending into said resilient material.

2. A flexible sub for connection in a drill string, said sub comprising:first and second axially aligned tubular members, a cylindricalextension of reduced outside diameter on an end of the first saidmember, a cylindrical socket within an end of the second said member andreceiving said cylindrical extension, the axial lengths of said 3 4, lsocket and said extension being substantially equal, the extension, andresilient material Within said holes and extending end of saidcylindrical extension being in subaround the portions of said pinsreceived therein. stantial abutting contact with said second tubularmember, References Cited in i file of this patflnt resilient materialbetween the cylindrical wall of said socket and the cylindrical surfaceof said extension, means 5 UNITED STATES PATENTS transmitting torqueloads'from one said member to the 2,620,165 Crickmer Dec. 2, 1952 othersaid member, said means being comprised of radially 2,765,147 VertsonOct. 2, 1956 disposed pins carried by said cylindrical socket and re-2,795,398 Ragland June 11, 1957 ceived within radially disposed holes insaid cylindrical 2,900,809 Crankshaw Aug. 25, 1959

1. A FLEXIBLE SUB FOR CONNECTION IN A DRILL STRING, SAID SUB COMPRISING:FIRST AND SECOND AXIALLY ALIGNED TUBULAR MEMBERS, A CYLINDRICALEXTENSION OF REDUCED OUTSIDE DIAMETER ON AN END OF THE FIRST SAIDMEMBER, A CYLINDRICAL SOCKET WITHIN AN END OF THE SECOND SAID MEMBER ANDRECEIVING SAID CYLINDRICAL EXTENSION, THE AXIAL LENGTH OF SAID SOCKETAND SAID EXTENSION BEING SUBSTANTIALLY EQUAL, THE EXTENDING END OF SAIDCYLINDRICAL EXTENSION BEING IN